The seven string guitar that our guy is talking about is a different ball of wax--I think. PG--Bucky Pizzarelli played his amazing jazz on a seven string, with a low B string to fill out the bottom, and there were a couple of others in the NYC area who emulated him. The legendary Bob Benedetto made them, I think, though I am not sure who made BP's original.

I knew someone who had one made--it was a big deal, and supposed to expand his musical horizons and all, but he found it cumbersome to play, what with having to worry about fretting an extra string all the time, and ended up leaving it in the closet most of the time.

My friend was also well regarded as a teacher, but he tended toward Blind Blake and such things. No names.